Backplates of vehicle disc brake pads essentially perform two functions. For one, they provide a solid support for slidably mounting friction material within a brake carrier in such manner to transmit shear loads induced on the friction material during braking to the brake carrier. Additionally, they transmit and distribute the pressure applied by brake tappets during braking evenly to the surface of the friction material to ensure even wear of the friction material over its service life.
In order to perform the first of these two functions, it is common to employ a resilient member, such as a leaf-type spring, to hold the brake pad radially in the brake carrier while permitting movement toward and away from an associated brake disc to prevent rattling of the brake pad in use. A positive location feature is usually provided on the backplate to ensure that the friction material is securely attached to the backplate. For example, the positive location feature can be holes or recesses into which the friction material can extend or steel mesh welded on to the backplate around which the friction material may be formed.
Each brake is generally provided with one or more tappets that apply the braking force over a small area relative to the total area of the backplate. To distribute the pressure from the brake tappet(s), it has previously been necessary to provide a relatively thick solid steel backplate that is punched or otherwise cut from steel sheet and is resistant to bending. Alternatively, an intermediate spreader plate has been employed to distribute the load over a thinner, although still substantial, backplate. A thick backplate constitutes a substantial proportion of the overall mass of the brake pad when unworn (e. g., approximately 30%). Once the friction material wears away in use, the backplate is usually thrown away. Reducing the mass of the backplate will result in environmental benefits and a reduction in the cost of materials. A lower backplate mass additionally means that a lower strength, and therefore lower mass (and a potentially lower cost) pad spring may be sufficient to hold the backplate in place.
A further disadvantage of prior art backplates for heavy vehicles is that high capacity stamping machines are required to manufacture the backplates, and consequentially a high capital investment is required to set up a manufacturing plant.
The present invention seeks to overcome, or at least mitigate, the problems of the prior art.